A loudspeaker module is an important acoustic component in a portable electronic device and used to perform the conversion between an electrical signal and a sound signal, and serves as an energy conversion device. A loudspeaker module usually comprises a module casing in which a loudspeaker unit body is received, and the loudspeaker unit body needs to be fixed in a module inner cavity by a positioning structure. In the current loudspeaker module, the positioning of the loudspeaker unit body in the module inner cavity is usually ensured by the squeezing between a retaining wall disposed on the module casing and the upper and lower casings of the module. However, as portable electronic devices constantly become light-weighted, thinner and slimmer, the loudspeaker module must become increasingly thinner and smaller and therefore the space in the loudspeaker module becomes increasingly smaller and smaller. If the retaining wall is still used for positioning in the increasingly smaller module inner cavity, it occupies a very large portion of the module inner cavity space, so the acoustic cavity of the module is reduced and the acoustic performance of the loudspeaker module falls.